[erlang-questions] builtin regexp functions in Erlang/OTP R12B-3

Tuncer Ayaz <>
Tue Jun 17 12:13:08 CEST 2008


On Tue, Jun 17, 2008 at 11:08 AM, Mats Cronqvist
<> wrote:
> Bjorn Gustavsson wrote:
>> Mats Cronqvist <> writes:
>>
>>
>>>   i think not allowing backreferences is the correct choice for erlang.
>>> after all, erlang is about reliability. and it seems not being
>>> POSIX-compliant has worked for 20 years.
>>>
>>
>> Note that Patrik has implemented the re BIFs to be rescheduable,
>> meaning that even a badly written regular expression will not prevent
>> the emulator from running other Erlang processes (even in the non-SMP
>> emulator).
>>
>
>  that is of course an example of the sound thinking that makes the
> emulator the excellent product it is.
>  even so, if i was responsible for, say, a telecom server product, i
> would be worried about a feature (backreferences) where it's so easy to
> slip up and peg the CPU at 100%. i would imagine that my application
> would run into problems if someone wrote a regexp that used up a CPU-second.
>
>> As noted in the EEP, some regexp libraries would have been hard or
>> impossible to make rescheduable.
>>
>
>  a crucial point. fwiw, i think using PCRE is a sound decision. the
> only reasonable alternative i'm aware of is the plan 9 regexp lib. did
> you look at that?
>  "Libregexp9 is a port of Plan 9's Unicode-capable regular expression
> library. It is small and simple and provides the traditional extended
> regular expressions (without modern complications like {} and various \x
> character classes). It supports Unicode via wide character or UTF-8
> encoding."
>
> http://swtch.com/plan9port/unix

I hope you guys don't mind me mentioning that if we discuss
regex implementations we should at least make sure to use
one with an implementation that uses NFAs. That should not be too hard.

http://swtch.com/~rsc/regexp/regexp1.html (Thompson NFA info)
http://en.wikipedia.org/wiki/Comparison_of_regular_expression_engines



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